Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
A type of wireless communication system using multiple antennas to transmit copies of a data stream across a number of antennas may be referred to as a transmit diversity wireless communication system. A transmit diversity wireless communication system may space-time modulate encoded portions of a data stream (e.g., encoded data blocks) to improve reliability of data-transfer between a transmitter and a receiver. A typical scheme to space-time modulate an encoded data block may include first and second periods of time over which a first copy of an encoded data block is transmitted from a first antenna and a second copy of the encoded data block is transmitted from a second antenna via a communication channel. The encoded block may be spread using orthogonal spreading codes. This type of space-time modulating of an encoded spread data block may be referred to as space-time spreading (STS).
Some transmit diversity wireless communication systems using STS may be designed with an assumption that a communication channel is at least quasi-static (e.g., has little to no variation or is substantially correlated) between each period of time over which copies of encoded data are transmitted. However, the present disclosure recognizes and appreciates that communication channels may undergo natural time variations caused by a physical environment in which the wireless communication channel is to be employed (e.g., effects of scattering, reflection, refraction, etc.). Further, rapid relative movement between a transmitter and a receiver may cause communication signals associated with a wireless communication channel to rapidly fade and thus further change or cause variations in the communication channel between transmit time periods. As a result of natural time variations and rapidly fading environments, reliability of data-transfer between a transmitter and a receiver can be problematic in a transmit diversity wireless communication system using STS that is designed with an assumption that a communication channel is quasi-static.
Some attempts to design a transmit diversity wireless communication system using STS that may account for variations in a communication channel assume that variations in the communication channel occur independently or have no correlation. However, variations in the communication channel may have some correlation. A correlation may decrease when a communication channel is employed in a rapidly fading environment. As a result of the existence of time correlation in a wireless channel, reliability of data-transfer between a transmitter and a receiver may also be problematic in a transmit diversity wireless communication system using STS that is designed under an assumption of no correlation between transmit time periods.